Various printing processes are used to produce various types of printed products and may be divided into three main categories:                letterpress printing        planographic printing (or even offset printing) and        gravure printing.        
In letterpress printing, the printing ink is transferred to the substrates from hard raised letters which are covered with a thin layer of ink by rubber rollers. The printing ink has to be formulated in such a way that it dries relatively slowly and does not begin to harden prematurely. Viscous slow-drying printing inks are required for modern high-speed newspaper printing machines using the rotary letterpress process.
In offset printing, the image to be reproduced is fixed on printing plates in the form of zones of opposite polarity. The hydrophobic viscous printing ink only wets the hydrophobic areas of the printing plates.
In gravure printing, the motif is engraved into the printing plate. After the printing plate has been wetted with the relatively low-viscosity printing ink, the surface is stripped so that printing ink is only left in the engraved depressions from which it is then transferred to the substrate to be printed.
The described examples show that printing inks have to meet a large number of requirements. The principal constituents of a printing ink are pigments, binders, solvents and additives with which the required properties of the printing inks are modified. Depending on the application envisaged for the printing ink, its viscosity, flow behavior and tack, for example, can be adjusted in this way.
The various requirements which the physical properties are expected to meet, particularly in the case of large-run printed products, impose stringent demands on the solvent used in the printing ink. On the one hand, it must be able to dissolve or disperse various binders (resins) and various additives; on the other hand, it should enable the viscosity of the printing ink to be adjusted to the required range.
In the past, mineral oils were originally used to a large extent as solvents for printing inks, mainly on cost grounds. This was unsatisfactory for a number of reasons so that there has long been a need to use mineral oil substitutes as solvents for printing inks. For about a decade now, certain fatty acid esters have often been proposed as solvents for printing inks. However, there is still a permanent demand for new developments in this field.
WO-A-90/03419 (Aarhus Oliefabrik) describes the use of C1-5 esters of aliphatic C8-22 monocarboxylic acids for removing grease, inks and other soils from printing machines.
JP-B2-3,317,512 (Nisshin Oil Mills) describes solvents for planographic and letterpress printing inks which contain as their principal constituent fatty acid monoesters of which the fatty acid component contains 6 to 22 carbon atoms and the alcohol component 1 to 4 carbon atoms.
U.S. Pat. No. 5,104,567 (A/S Alaska Gruppen) describes cleaning fluids for removing printing inks from printing machines, these cleaning fluids containing a vegetable oil and an emulsifier in the form of a surfactant.
WO-A-96/34920 (Henkel KGaA) describes solvent compositions for printing inks. The compositions contain (a) dearomaticized mineral oils, (b) esters of C8-22 fatty acids and/or (c) C6-36 fatty alcohols.
U.S. Pat. No. 4,357,164 (Sakata Shokai Ltd.) describes printing ink compositions containing high-boiling solvents in combination with esters based on C4-10 fatty acids, oleic acid and elaidic acid.
U.S. Pat. No. 5,122,188 (The United States of America) describes printing inks based on heat-treated oils, the heat treatment leading to polymerization products with a molecular weight above 26,000.
U.S. Pat. No. 5,340,493 (R. J. Principato) describes cleaning compositions for removing printing inks from machine parts used in the printing industry. The ternary compositions contain esters of tall oil fatty acids, organic solvents and surfactants.
U.S. Pat. No. 5,178,672 (Canadian Fine Color Company) describes a carrier medium for paste-form printing inks, this carrier medium containing esters based on vegetable fatty acids and simple alcohols or glycols as solvent. The vegetable fatty acids are understood to be those which occur naturally in oils of vegetable origin, i.e. which have not been subjected to further chemical modification. The main representatives of the described class of fatty acids are mentioned in column 2, lines 32–37. They are saturated and olefinically unsaturated linear fatty acids.
U.S. Pat. No. 5,427,615 (Arizona Chemical Comp.) describes a process for the production of a gel-form printing ink composition, a fatty acid ester being used as solvent (step B). The fatty acid constituent of the ester comprises C8-24 fatty acids while the alcohol constituent comprises alcohols or glycols containing 1 to 10 carbon atoms, with the proviso that the fatty acid emanates from oils which occur in linseed oil, soybean oil and rapeseed oil.
U.S. Pat. No. 5,173,113 (Topez Comp.) describes printing ink compositions which contain di- or oligoesters of olefinically unsaturated fatty acids and di- or polyfunctional acrylate esters as functional constituents.
U.S. Pat. No. 5,713,990 (The United States of America) describes printing ink compositions based on a ternary mixture: (1) a resin or heat-treated (and hence polymerized) oil, (2) a non-heat-treated vegetable oil and (3) at least one fatty acid ester based on unsaturated fatty acids, more particularly linoleic acid and linolenic acid. Component (3) is present in minor amounts.